1. Field of the Invention
This invention generally relates to a rotational or angular phase control apparatus provided between an input shaft and an output shaft for varying the mutual rotational or angular phase between input and output shafts. For example, this invention can be applied to a valve timing control apparatus for an internal combustion engine which varies a rotational or angular phase of a cam shaft with respect to a crank shaft to vary the valve opening or closing timing for at least one of intake and exhaust valves.
2. Related Art
In ordinary internal combustion engines, rotation of a crank shaft is transmitted to a cam shaft by way of a timing belt, or a chain, or a gear. There are known some engines which comprise a valve timing control apparatus interposed between the crank shaft and the cam shaft to vary the rotational phase therebetween for varying the open-or-close timing of at least one of intake and exhaust valves. Such an apparatus is referred to as VVT (variable valve timing apparatus).
The U.S. Pat. No. 4,858,572 (corresponding to Unexamined Japanese Patent Application No. HEI 1-92504, published in 1989) discloses this kind of valve timing control apparatus.
According to this conventional apparatus, a rotor is accommodated in a timing pulley. The rotor is provided with a total of six vanes each associated with a hydraulic chamber. Of six hydraulic chambers, three are communicated with one oil passage and the remaining three are accommodated with the other oil passage. These two oil passages are formed in the rotor, thereby supplying pressurized oil to each hydraulic chamber and causing a volume change in each hydraulic chamber. In response to this volume change of each hydraulic chamber, the rotational or angular phase of rotor can be varied with respect to the timing pulley.
Furthermore, this conventional apparatus comprises two knock pins serving as locking members. When the rotor is positioned at the most-advanced position or the most-retarded position, the rotor is locked with the timing pulley by either of these two knock pins.
According to this conventional apparatus, knock pins are disposed in radial directions so as to shift in radial directions. Hence, there is the possibility that these knock pins may be erroneously shifted in the radial direction when subjected to a large centrifugal force derived from rotation of rotor. In general, the arrangement of radially shiftable knock pins tends to enlarge the overall diameter of the apparatus, getting the downsizing of the apparatus difficult.
As knock pins are accommodated in the timing pulley, it is necessary to provide bolts protruding from the outermost end of the apparatus for closing the housing of the rotor. This also makes it difficult to reduce the size.
The configuration of each knock pin is a simple rod which is likely to fail to smoothly engage or enter into a coupling bore. Alternatively, if a large clearance is provided between the knock pin and the coupling bore to assure smoothness, noises will be caused due to the looseness of the knock pins.
Furthermore, there is the possibility that each knock pin of a simple rod may be deformed when received a strong stress acting in both of the rotational directions.
One knock pin is moved by one hydraulic pressure, while the other knock pin is moved by the other hydraulic pressure. When the valve timing is set at an intermediate position, or during the switching operation of knock pins, knock pins may be frictionally slide on the surface of the rotor. It will promote the wear and worsen the durability of frictional parts, while increasing operational resistances.
Moreover, if one of knock pins is damaged, the valve timing will be fixed at either one the most-retard position or the most-advanced position. If the valve timing is accidentally fixed at and not escapable from the most-advanced position (which is the valve timing preferably used for high engine speeds and improper for an idling or low engine speeds), it will result in the difficulty in the starting-up operation of the engine.
Yet further, according to the above-described apparatus, a plurality of oil passages are formed in the rotor so as to extend in the radial directions. A groove, serving as an oil passage, is also formed on the outer cylindrical wall of the rotor. Such oil passage arrangement forcibly requires complicated machining and drilling operations in manufacturing the outer surfaces of the rotor.
Still further, provision of six vanes complicates the configuration of the apparatus. In this respect, the U.S. Pat. No. 5,289,805 discloses a two-vane type rotor. However, the conventional two-vane type rotors are encountered with the difficulty in acquiring a satisfactory pressure-receiving area and a durable housing strength.